This invention relates to a fuel supply control system for an internal combustion engine, and more particularly to such a control system, which can properly control a fuel quantity to be supplied to the engine at the start of the engine.
Fuel supply control systems for an internal combustion engine are known e.g. from Japanese Patent Publications No. 57-27972 and 60-29824, in which excessive enrichment of an air/fuel mixture to be supplied to the engine at starting, and smoldering of ignition plugs which are wetted with fuel due to the excessive enrichment, are prevented in order to improve the startability of the engine.
According to the Japanese Patent Publication No. 57-27972, the opening of a throttle valve in the intake passage of the engine is detected at the start of the engine, and fuel supply to the engine is reduced or cut off immediately upon detection of the opening motion of the throttle valve from a closed position to an open position. However, if the driver already depresses the accelerator pedal just before the start of the engine so that the throttle valve is already open at the start of the engine, or if the throttle valve is erroneously detected to be already open at the start of the engine due to the malfunction of a throttle opening sensor, fuel supply is immediately reduced or cut off immediately upon turning on the starter, and consequently a quantity of fuel sufficient for causing firing within combustion chambers cannot be supplied, resulting in failure to start the engine.
According to the Japanese Patent Publication No. 60-29824, a fuel quantity to be supplied to the engine at starting is controlled to be gradually reduced in accordance with the number of crank angle pulses generated from the start of the engine. However, according to this method, it takes much time until the fuel quantity is sufficiently reduced. As a result, an enriched air/fuel mixture is supplied to the engine for a long time after the start of the engine, so that ignition plugs continue to smolder, resulting in failure to start the engine.